Method for digesting solid car



Sept. 26, 1939. w. MCK; BYWAT'ER' 2,174,184

METHOD FOR DIGESTING SOLID CARBONACEOUS MINERALS Filed May 11, 1938INVENTOR ATTOR Y Patented Sept. 26, 1939 PATENT OFFICE METHOD FORDIGESTING SOLID CAR- BONACEOUS MINERALS Wilfred McKinley Bywater,Weehawken, N. J., assignor to The Barrett Company, New York, N. Y., a.corporation of New Jersey Application May 11, 1938, Serial No. 207,350

Claims.

This invention relates to the manufacture of heat-digestion productsfrom carbonaceous mineral materials such as bituminous coal, cannelcoal, shale, and the like under conditions 'such that a substantial butregulated amount of decomposition of the carbonaceous mineral materialstakes place during the digestion.

In the past it has been proposed to prepare such products by introducingthe mineral material into a tank containing a body of a hydrocarbonliquid, such as coal tars, high-boiling coal tar oils, and coal tarpitches, or various petroleumtars and oils, and then to heat the tankexternally to bring the temperature of the mixture to between 300 and400 C. Such processes were subject to the disadvantage that since a muchhigher temperature prevailed at the tank wall suriaces than in the bodyof liquid, solid material in contact with the surfaces was subjected tomore intense heat-treatment thansolid material at a distance therefromand conseuuently overheating. and even charring of the solid materialoccasionally occurred, and deposit of carbonaceous scale on the walls ofthe vessel resulted.

Moreover, successful operation of the digestion process requires carefulcontrol to effect the desired degree of decomposition of-the mineralundergoing digestion, e. g. coal. It has been found that if thedigestion is carried out so that no decomposition or only incipientdecomposition of the coal occurs, products are obtained of a quitedifferent nature from those desired. It, however, the time andtemperature of digestion oi a given coal are increased, a relativelysudden change occurs in the consistency of the product together withmarked evolution of typical volatile coal-decomposition products and areduction in the content of volatile combustible matter in the digestedmineral.

Commercially desirable products are obtained by carrying the digestionto or beyond the point x dilutes the desired and characteristic finalproduct with material approaching ordinary pitch in character.

direct-fired tank-still process, it has been proposed to circulate theliquid hydrocarbon through a body of coal or other carbonaceous mineralmaterial. In the process thus proposed the hydrocarbon liquid fiowecl ina circuit involving a heater and a digestion chamber, so that heating ofthe liquid was accomplished at a point out of contact with the main bodyof coal which it was desired to subject to the digestion treatment. Thisprocess was found to overcome the disadvantages of overheating,excessive decomposition and the formation of carbonaceous scale onheating surfaces. In operation of the process on a large In order toovercome the disadvantages of the v scale, however, it was frequentlyfound that after a run a varying percentage of the coal remained in thedigestion chamber in a partially digested condition. Since theproperties oi the desired product depend to a considerable extent on thecontent oi digested coal, this had two disadvantages:

(ll the properties oi the product of the original batch could not beaccurately predicted because its digested-coal content was thedifference between the coal introduced (less volatile decompositionproducts) and the varying residue in the digester, and there was no wayof determining accurately beforehand the proportion of the! coal thatwould remain as residue;

(2) in formulating succeeding batches it was impossible to maizeallowance for the varying residue in the digester, part of which wouldbe dispersed in each following batch, for there was no ready means formeasuring or weighing the residue in situ.

Still another disadvantage encountered lay in the fact that the partialydigested coal possessed a semi-liquid, livery, or jclly -liire charactersuch that it formed a more or less resistant protective coatingonfragments oi undigested coal, and contact oi liquid therewith wasdiminished. As a consequence the digestion was appreciably prolonged.

"While the above discussed disadvantages are not of a nature to make theprocess unworkable, they lead to products of widely variant propertiesand make it uneconomical for producing products to close specifications.

In accordance with the present invention it has been found that thedesired degree of decomposition of the carbonaceous mineral can beeffected, Wh le the disadvantages of both the direct-fired tank-stilldigestion and the methodinvolving circulation oi" liquid hydrocarbonthrough the carbonaceous mineral may be eliminated, by subiecting themineral in a finely divided condition to heating while suspended in a'turbulent stream of the liquid. 'Ihis is accomplished by mixing thefinely divided mineral with the hydrocarbon liquid and the mixture at avelocity above its critical velocity through a ,tubular heater orequivalent heating device.

By'the process of this invention it is possible to prepare compositions,suitable for use as paving compositions, road binders, block fillers,roofing compositions, water-proof paints, etc., possensing not only ahigh degree of uniformity throughout a particular batch but having aminimum of variation between batches.

Apparatus for conducting the process of the present invention isillustrated in the accompanyim thawing.

The ninneral I designates a tank for mixing the carbonaceous mineralmaterial and' the liquid hydrocarbon. An agitator l, driven by motor I,may be provided for stirring the contents of tank I. The agitator 2 maybe provided with a drag chain I for cleaning the walls of the tank, ifdesired, especially if the tank is arranged with external heating means(not shown) to bring it to reaction temperature. The agitator may eitherrotate or oscillate, as desired. A pipe I leads from tank I, near thebottom thereof, to

pump I. From pump a pipe I, having avalve 0, leads to a tubular heatingcoil 0 arranged to be heated by hot combustion gases. An outlet pipe I.having avalve II is dispoud on pipe I between the ,pump and the heatingcoil. A re- .turn line "leads from the heating coil back to I has aninlet pipe It provided with a valve It for introducing hydrocarbonliquid and a hopper II, which has a suitable closure It, for theintroduction of solid carbonaceous mineral matter. If preferred, a starvalve or other suitable closure permitting introduction of solidmaterial while avoiding escape of substantial quantitiesofvaporamaybeprovidedinplaceofthe simple closure ll.

Avapor pipe ll leads fromtank I to condenser II cooled by water, tar tobe used-in a succeeding digestion, or another suitable cooling medium.Oondensate outlet II leads to oil storage (not shown);

Athermometerwelillisdisposedintank I to indicate the temperature of theliquid therein.

pparatus may be provided with the customary clean outs. traps,insulation, etc.

'lheaboveapparatus maybeoperatedinthe following manner:

moo gallons of topped-tar-and-heavy-tar-oil- 7 having an initial boilingpoint aroimd C.ar'echargedtotank I throughinlet ll; is then closed. Pump8 is started as enough of the mixture is introduced to pump supplied.The mixture is circulated through heating coil 9 and recirculated to theextent necessary to heat it to a temperature around 150 C. as indicatedby the thermometer in well 20. Finely divided coal, having a particlesize not over 0.3 cm. in diameter is then introduced at I 5, theagitator being operated to 'mix the coal withthe liquid contents of tankI When the desired amount of coal has been added, normally 5% to'45% of'the tar-tar-oilmixture, depending upon the type of product it isdesired to produce, the temperature of the mixture in tank I may haverisen to between 170 and 210 C. and the mixture leaving coil 8 may be atatemperature between 200 C. and 250 C. as recorded by the thermometer inwell Ila. Agitation of the contents of the still and circu lation of thetar containing suspended coal particles are continued until the desiredmaximum digestion temperature, usually somewhere between 300 and 320 0.,is obtained.

For illustration a tubular heater containing 93 tubes each 2% inches indiameter and about 8% feet long connected serially by return bends wasfound to attain the desired temperature, measured from the time ofcompleting the coal charge, in from 5 to 6 hours. The average linearvelocity of the mixture (topped-tarand heavy- 'oil-mixture plus 20% ofcoal particles of less than 0.3 'cm. diameter) through the heater was 11to 12 feet per second, as compared with a critical velocity for themixture in this apparatus believed in the neighborhood of 1 foot persecond. Since the critical velocities of the tarcoal mixtures ofcommercial importance at the digestion temperature are in the sameneighborhood, it may be said that in general the average linear velocityof the mixture within 1% inch of the heating surface should be above 1foot per second. This generalization, however, would not include thosecases where turbulence is induced by use of surfaces other than heatingsurfaces or by use of heating tubes of substantially smaller than 2%inch diameter or otherwise.

The temperature at Ila at the start may be 80 to '75? or more above thatat 20. Fairly satisfactory products have been produced when the mixturehas been permitted to absorb heat at about this rate throughout theprocess and it is possible to maintain a diilerential of as much as 100'between the temperatures at Ila and 20. However, it is preferred toavoid so high a temperature diii'erence, at least near the maximumdigestion temperature. It has been found" that a temperature differenceof about 20 makes the most satisfactory products.

For an apparatus of the above proportions handling an 8000-8500 galloncharge containing coal which undergoes the desired conversion at about305' C., the temperatures measured by thermometers at Ila andllfrespectively may correspond as follows:

lie 20 Donna Duran mas 100i!) 110 2:05:20 am His-= 810 2001110 3181: 88061i: 6

themaximum temperature to be attained by the mixture, for thegas-to-liquid temperature difierence becomes radically less as thetemperature of the liquid rises. In case the gases are at hightemperatures on the order of 1000 to 2000 C. the reduction in heatingefiect as a consequence of reduced temperature difference will be smalland to keep the liquid temperature down the liquid may, be circulated atan increased rate or the heat supply may be reduced, as by diluting thecombustion gases with air or cutting the flow of fuel. In this mannerthe maximum temperature of the liquid at I2a may be kept within 10 or 20of the maximum liquid temperature in the tank as recorded at 20.

The following example illustrates the preparation of a coal-digestionproduct by the process of the present invention:

6889 gallons of a digestion medium consisting of toppedhigh-temperature, bituminous coal tar and heavy creosote oil werecharged to tank I as above described. The temperature was brought up tosomewhat above. 150 C. by circulating the tar-oil mixture throughheating coil 9 by means of pump 6 from and to tank I. While the mixturewas being circulated, 18,671 pounds bituminous coal, ground to pass a 10mesh screen, were gradually introduced into tank I and there agitatedwith the tar-oil mixture. The liquid flow through coil 9 was maintainedat 'a constant average rate of 11.60 linear feet per minute during thedigestion. Laboratory tests having previously been made to determinesuitable digestion temperature for the coal in question to secure thedesired degree of coal decomposition, heating and circulation werecontinued to bring the contents of tank I as recorded at 20 to 304 C.over a period of several hours; at the same time the the followingproperties.

Melting point C '10 Penetration at (200 gms., 30 seconds) l4- 25 (100gms., seconds) 30 46.1 (50 gms., 5 seconds) 80 Slide test at 40 -C. ('7hours, 30 angle, /2

inch cube) "inches" 2 I claim:

1. The method of producing from coal and petroleum tars, pitches oflower temperature susceptibility than ordinary tar pitches of the samemelting point, comprising suspending finely pulverized coal in regulatedamount in a liquid comprising tar, of the group consisting of coal tarand petroleum tar, or its distillation products,

which liquid is capable of forming pitch on distillation, agitating saidliquid and mechanically suspended coal, recirculating said liquid andcoal through a heating coil to effect the decomposition of the coal, andcontinuing the decomposition process until a pitch product of thedesired melting pointand temperature susceptibility is obtained.

2. The method of digesting bituminous coal in a coal-tar digestionmedium, which comprises preparing a mixture of the digestion mediumcontaining the coal suspended therein in finely divided form,withdrawing a portion of the mixture, passing a stream thereof whilefree from added reagents through a heating zone at a rate such that theaverage velocity of the mixture within one and a quarter inch of theheating surface is above one foot per second, returning it to the mainbody of the mixture and mixing it therewith, and continuing saidoperation only until the temperature of the main body of the mixture hasreached but not exceeded a digestion temperature between 300 and 400 C.

3. The method of producing from tar, pitches of lower temperaturesusceptibility than ordinary tar pitches of the same melting point,comprising suspending finely pulverized coal in regulated amount in aliquid comprising bituminous coal tar or its distillation products,which liquid is capable of forming pitch on distillation, agitating saidliquid and mechanically suspended coal, recirculating said liquid andcoal through aheating coil to effect the decomposition of the coal, andcontinuing the decomposition process until a pitch product of thedesired melting point and temperature susceptibility is obtained.

4. The method of producing from coal tar, pitches of lower temperaturesusceptibility than ordinary tar pitches of the same melting point,comprising suspending finely pulverized coal in regulated amount in aliquid comprising coal tar and creosote oil, which liquid is capable offorming pitch on distillation, agitating said liquid and mechanicallysuspended coal, recirculating said liquid and coal through a heating,coil to effect f the decomposition of the coal, and continuing thedecomposition process until a pitch product of the desired melting pointand temperature susceptibility is obtained.

5. The method of digesting bituminous coal in a coa1tar digestionmedium,which comprises preparing a mixture of a digestion medium comprisingbituminous coal tar and heavy creosote oil containing the coal suspendedtherein in finely divided form, withdrawing a portion of the mixture,passing a stream thereof while free from added reagents through aheating zone at a rate such that the average velocity of the mixturewithin one and a quarter inch of the heating surface is above one footper second, returning it to the main body of the mixture and mixing ittherewith, and continuing said operation only until the temperature ofthe main body of the mixture has reached but not exceeded a digestiontemperature between 300 and 400 C.

WILFRED McKINLEY BYWATER.

